Diffraction process photography and reconstruction: fidelity enhancement by minimization of crosstalk and moire patterns

ABSTRACT

This disclosure depicts methods and structures for multiplex information photorecording and retrieval with minimization of interference between information channels. More particularly, this disclosure concerns diffraction process methods and structures for recording a plurality of images in superposition on a common recording medium each modulating an azimuthally distinct spatial carrier, and selectively retrieving the component images in a coherent projection system. Stress is placed upon predetermining the spatial frequency and azimuthal orientation of each of the carriers such that interchannel interference during projection is minimized.

United States Patent Bouche Feb. 8, 1972 [54] DIFFRACTION PROCESSPHOTOGRAPHY AND RECONSTRUCTION: FIDELITY ENHANCEMENT BY MINIMIZATION OFCROSSTALK AND MOIRE PATTERNS I72] Inventor: Edmund L. Bouche, Lexington,Mass.

[73] Aimigncc: Technical Operations, Incorporated,

Burlington, Mass.

I').').| Filedv July 22, I969 [2|] Appl. No; 843,312

[52] U.S. Cl. ..96/27 H, 355/32 [51 Int. Cl. ..G03b 33/00 [58] Field ofSearch ..96/24, 25, 27 H, I7, 118; l78/5.4; 340/324; 355/32; 95/122 [56]References Cited UNITED STATES PATENTS 3,504,606 4/1970 Makovsky..355/7l Primary ExaminerN0rman G. Torchin Assistant Examiner-Alfonso T.Suro Pico AttorneyRosen &-Steinhi1per and John H. Coult ABSTRACT Thisdisclosure depicts methods and structures for multiplex informationphotorecording and retrieval with minimization of interference betweeninfonnation channels. More particularly, this disclosure concernsdiffraction process methods and structures for recording a plurality ofimages in superposition on a common recording medium each modulating anazimuthally distinct spatial carrier, and selectively retrieving thecomponent images in a coherent projection system. Stress is placed uponpredetennining the spatial frequency and azimuthal orientation of eachof the carriers such that interchannel interference during projection isminimized.

34 Claims, 13 Drawing Figures msmaorca a ma 3.640.7i1

SHEET 1 OF 3 BLUE RED WHITE CYAN YELLOW l l l I MAGENTA GREEN 22 Q F|G.2FIG. 3

WHITE GREEN RED BLUE FILTER RED BLUE 46 GREEN FILTER RED FILTER BLUEFILTER FIG. 4 28 Bw EDMUND L. BOUCHE" INVENTOR FIG. 5 By- ROSEN857'57IVH/LPER on JOH/VHCOULT ATTORNEYS Pmmsnm 8M2 3.640.711

SHEET 2 OF 3 INVENTOR By= ROSEN a STg/NH/L PER Q n JOHN H. COUL rATTORNEYS EDMUND LBOUCHE DIFFRACTION PROCESS PHOTOGRAPHY ANDRECONSTRUCTION: FIDELITY ENHANCEMENT BY MINIMIZATION OF CROSSTALK ANDMOIRE PATTERNS BACKGROUND OF THE INVENTION Diffraction processphotostorage and retrieval systems have been explored sporadically formany years. Robert W. Wood is credited by Herbert E. Ives as havinginvented the color diffraction process in 1899. The Wood process (US.Pat. No. 755,983) involves the formation of a composite photographicrecord on which red, blue, and green color. separation images modulatespatial carriers of like orientation but different spatial frequency.The frequencies of the spatial carriers are selected such that uponretrieval in a coherent projection system an aperture at the location ofthe first spectral order in the Fourier transform space will receivefrom each area of the photograph only radiation from the region of thedispersed spectrum produced by the carrier on that area whichcorresponds to the color of the scene information recorded thereon. i v

In 1906 Herbert E. Ives attempted to overcome certain crosstalk effectsin the Wood system caused by nonlinearities in the photographicrecording processes used by avoiding overlapping of red, blue, and greencolor separation images. Overlap was avoided by sampling each of thecolor separations at like periodic intervals and interlacing them with a120 phase displacement to form the composite record. The colorseparation images were impressed upon spatial carriers of likeorientation and different frequency, or like frequency and differentorientation to enable the images to be separated by optical Fouriertransformation techniques. The Ives system, however, was difficult toimplement except in the laboratory under carefully controlledprocedures, and is not adaptable to general photographic applications.

Yet another problem associated with diffraction process systems involvesthe formation of interference patterns, commonly referred to as Moirebeats or patterns in retrieved images which result from the overlap inthe Fourier plane of energy from separate information channels. Theprior art is not known to have addressed itself to the solution of thisproblem.

OBJECTS OF THE INVENTION It is an object of this invention to providesystems. and methods of diffraction process photography and reconstruction which allow the use of overlapped carriers but which provides forreconstruction of the photographed images with significantly lessinterchannel interference than is provided by prior art methods.

It is another object to provide methods and apparatus for spectral zonalphotography and reconstruction which is adaptable for generalphotographic applications and which provides reconstructions withminimal degradation due to crosstalk and Moire patterns.

It is another object of this invention to provide diffraction processmethods and apparatus of spectral zonal photography and reconstructionwhich yield displays of enhanced fidelity by utilizing the greatersensitivity of panchromatic photographic emulsions to radiation in thehigher energy region of the visible spectrum.

Further objects and advantages of the invention will in part be obviousand will in part become apparent as the following description proceeds.The features of novelty which characterize the invention will be pointedout with particularity in the claims annexed to and forming a part ofthis specification.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of theinvention, reference may be had to the following detailed descriptiontaken in connection with the accompanying drawings wherein:

FIG. I is'a distorted scale schematic perspective view illustrating therecording of a colored scene through a spectral but zonal filter so asto impress separate spectralizonal images on azimuthally distinctspatial carriers;

FIG. 2 is a schematic view of the spectral z'onal filter shown in FIG.I;

FIG. 3 is a distorted scale representation of the photographic recordformed in FIG. 1 through the FIG. 2 filter;

FIG. 4 is a schematic representation of a'coherent projection system forreconstructing the scene image in full color from the black-and-whitephotographic record shown in FIG.

FIG. 5 is an extremely simplified representation of the diffractionpattern which might be produced at the source image plane (the Fourierplane) in the FIG. 4 projection system, the diagram showing only thefirst spectral orders as they would be formed by a monochromatic pointsource, but not showing any crosstalk orders;

FIG. 6 is similar to FIG. 5 but shows the efi'ect on the diffractionpattern of using a polychromatic source;

FIG. 7 is a representation of the diffraction pattern shown in FIG. 6 asit might appear after beingspectrally-and spatially filtered in aprojection system such as is shown in FIG. 4;

FIG. 8 is an extremely simplified diagram corresponding to FIG. 5 butillustrating the crosstalk introduced when the photographic recordingprocess is nonlinear and the spatial carriers carrying the componentcolor separation images are overlapped",

FIG. 9 illustrates a spatially and spectrally filtered diffractionpattern as shown in FIG. 7 but includes only those crosstalk orderswhich are not capable of being blocked completely by spectral or spatialfiltering in the Fourier plane, and which interfere with the primaryspectral orders;

FIG. 10 is a diagram similar to FIG. 9 illustrating the reduction intransmitted crosstalk energy caused by increasing the spatial frequencyof the carrier for the green color signal Gm relative to the spatialfrequency of the Br and Rm carriers;

FIG. 11 is a diagram very similar to FIG. 10 but showing the effect ofincreasing the spatial frequency of the carrier Bw signal relative tothe spatial frequency of the remaining two carriers; '1

FIG. 12 represents the combined effect of 'concomitantly increasing thespatial frequency of the Gm andBw carriers; and

FIG. 13 illustrates, in accordance with the second aspect of thisinvention, the effect on crosstalk suppression of varying theorientation of one of the carriers.

DESCRIPTION OF THE PREFERREDEMBODIMENTS cally in FIG. 2, comprisesmutually coextensive periodic arrays of yellow, cyan, and magenta filterelements having direction vectors oriented at 45, 0, and 45,respectively. During the recording operation, the encoder 24 is causedto be multiplied with the object, or an image thereof, preferably bylocating the encoder 24 at the image plane of lens 23 in intimatecontact with photostorage material 20. The yellow, cyan, and magentafilter elements, respectively, act to impress blue, red, and green colorseparation information on spatial carriers whose vectorial directionsare --45, 0, 45 respectively. FIG. 3 represents a record as might beformed by the recording operation depicted in FIG. I. It is seen thatthe areas of the object 22 which contain pure primary color informationhave but a single carrier whose orientation is a function of theorientation of the filter array which is complementary to the the objectcontain three overlapped carriers. As will be discussed in detailhereinafter, it is the overlap of the carriers and the processing of thephotographic record in a nonlinear fashion which is the primary cause ofcrosschannel interference effects.

FIG. 4 illustrates in simplified schematic form, a coherent opticalprojection which might be used to reconstruct a full color display fromthe FIG. 3 record. The projection system comprises a light source forgenerating light which is spatially coherent at the film gate 28 at thefrequency of the spatial carriers employed. The light source is hereshown as comprising an arc lamp 30, a condensing lens 32 for imaging thearc into an aperture 34 of restricted diameter in a mask 36. Acollimating lens 38 and a transform lens 40 illuminate the film gate 28and form an image of the aperture'34 in a space commonly termed theFourier transform space at which appears a Fraunhofer diffractionpattern of the record 42. A projection lens 44 images the record 42 atan output plane 46. In order to detect the separate color channels andreintroduce the appropriate spectral characteristics in each of thecolor channels, a spatial filter 48 is located at the Fourier transformplane. The spatial filter 48 transmits only the first spectral ordersassociated with each of the red, blue, and green channels and containsred, blue, and green transmission filters in the filter openings suchthat the color separation information in each of the channels is causedto be transmitted to the output plane in visible radiation having theappropriate spectral characteristics. With a simple system such as isshown in FIG. 4, a full-color reconstruction of the photographed scenecan be produced from the encoded monochrome record 42.

The nature of the Fourier transform space and the effects that may beachieved by spatial and/or spectral filtering in this space may bebetter understood by reference to FIGS. -7. FIG. 5 is an extremelysimplified representation of a Fraunhofer diffraction pattern whichmight be formed by the FIG. 4 projection apparatus at the source imageplane. The diagram shows only the fundamental spectral orders; none ofthe crosstalk terms normally produced are shown. Further, the FIG. 5diagram assumes that the source is monochromatic and spatially coherent.The diagram further implies that the spatial carriers used were of equalfrequency and that the photostored image is bandlimited to less thanone-half the carrier frequency.

FIG. 6 is similar to FIG. 5 but attempts to schematically show theeffect of a polychromatic source in radially smearing of the spectralorders due to the wavelength dependence of diffraction phenomena, asexplained in more detail hereinafter. FIG. 7 represents the FIG. 6distribution after being spectrally and spatially filtered by the filter48 in the FIG. 4 system.

By the nature of diffraction phenomena, the diffraction angle a is: sin0PM) 1 where A represents the spectral wavelength of the illuminationradiation and 0) represents spatial frequencies. The diffracted spectralorders will be formed in the transform space at the delta functionpositions'determined by the transform of the record spatial carriers atradial distances from the pattern axis:

R==smw (2) where s is the image distance from lens 40; X is the meanwavelength of the illuminating radiation; m represents the diffractionorder; and w is the fundamental grating frequency.

The first orders of each of the diffraction patterns can be consideredas being an object spatial frequency spectrum of maximum frequency 0:,(representing a radius of the order) convolved with a carrier of spatialfrequency w The second order components (not shown) can be thought of asbeing the convolution of an object spectrum having a maximum spatialfrequency m, with a'carrier having a spatial frequency of 2m and soforth. Thus, the various orders of each diffraction pattern may bethought of as being harrnonically related, with a spacial frequency w oran integral multiple thereof, acting as a carrier for the spectrum ofspatial frequencies characterizing the object detail. First orderspectra only are shown in the drawings; however, it should be understoodthat second and higher orders are present, but these will be ofrelatively low intensity.

This invention is directed to the minimization of degradation inreconstructed scene images due to the transmission in the color channelsof crosstalk energy from another color channel; this invention is alsointended to lessen the effects of Moire beat patterns in reconstructedimages resulting from interference between transmitted, crosstalk energyand pure color channel energy.

FIG. 8 is an extremely simplified diagram of the FIG. 5 diffractionpattern but. including crosstalk orders caused by the use ofphotographic processing which is nonlinear, that is, processing to otherthan 'y=-2. For a detailed discussion on linear photographic recording,see Linear Multiple Image Storage}? by Peter F. Mueller, Applied OpticsFeb. 1969), Vol. 8, No. 2. In FIG. 8 the crosstalk orders are showncircumscribed by broken lines and are identified according to the colorsignals which interact to produce the particular crosstalk order. Forexample, the crosstalk term representing a mixture of the green and redcolor separation signals, Glu and Re, is labeled X The location of thecrosstalk orders can be found by adding vectors drawn from the origin tothe G00 and R00 orders. The crosstalk order X represents a mixture ofthe energy from adjacent primary spectral orders. Of greater concern arethe crosstalk orders produced by the combination of nonadjacent primaryspectral orders. For example, X' is a crosstalk order produced by thecombination of nonadjacent red channel and green channel energy (see thevectorial diagram illustrating X' as being located at the point ofvectorial summation of R'm and Gm).

It should be kept in mind that FIG. 8 is of the same order ofoversimplification as in FIG. 5 and that all of the assumptions madewith respect to FIG. have also been made with respect to FIG. 8 exceptfor the assumption of linearity in the formation of the scene record. Amore realistic perception of the nature of the diffraction pattern inthe Fourier plane can be realized by extrapolating the monochromaticrepresentation in FIG. 8 to a polychromatic representation. In the sameway that FIG. 6 illustrates the polychromatic extrapolation of the FIG.5 diagram, one can envision each of the illustrated primary spectralorders and. crosstalk orders in FIG. 8 as being but one of an infinitecontinuum of orders increasing in size and radial displacement, one foreach wavelength of the radiation emanating from the polychromatic lightsource in the projection system. An attempt to pictorially illustratethe more realistic polychromatic version of FIG. 8 has been avoided onthe basis that the diagram would be so complex as to be valueless.

It is helpful to keep in mind, however, that only crosstalk orders ofinterest are those which cannot be blocked by a mask or spectral filter.In the context of the extremely simple FIG. 4 system, the crosstalk ofinterest is that which will be transmitted through the filter 48. FIG. 9depicts a simplified diffraction pattern after being spectrally andspatially filtered including only those crosstalk terms which will betransmitted through the FIG. 4 to the output plane and which willtherefore cause image degradation.

In accordance with one aspect of this invention it has been found thatthe amount of crosstalk energy transmitted through the primary spectralorders can be dramatically reduced by preselecting the relative spatialfrequencies and azimuthal orientations of the carriers in such a way asto minimize the overlap of crosstalk orders with the spectral orderscarrying pure color separation information (hereinafter called primaryspectral orders).

FIG. 10 illustrates the effect on crosstalk suppression of increasingthe carrier for the green color separation signal Gm by approximately 20percent relative to the spatial frequency of the Rm and Boo carriers.The decrease in the amount of transmitted crosstalk can be appreciatedby comparing the areas of overlap of the crosstalk and primary spectralorders in FIG. 10 with the areas of overlap shown in FIG. 9. Thecrosstalk reduction is of even greater magnitude than is manifest from acomparison of FIGS. 9 and 10 since it must be realized that the energydistribution across these spectral orders is not constant, but ratherhas a Gaussianlike distribution with a relatively rapid fall-off at theperipheries thereof.

It is also important to note that not only have the areas of overlap ofthe crosstalk and primary spectral orders been decreased by increasingthe relative spatial frequency of the green information carrier, butalso that the spatial displacement between the interfering orders hasbeen increased, causing the Moire beat frequency (the spatial frequencyof the Moire pattern) to increase. Increasing the Moire beat frequencyis desirable from the standpoint that the contrast of the patternbecomes less as its frequency approaches the cut off of the transferfunction of the viewing, recording, or display system employed.

FIG. 11 shows the effect of increasing the spatial frequency of thecarrier for the blue signal Bw relative to the carrier frequencies ofthe red signal and the green signals. Again, by way of example only, theincrease in the B01 carrier frequency has been shown to be roughly 20percent.

FIG. 12 shows the effect of increasing the spatial frequency of thecarriers for both the green signal Go) and the blue signal Bw byapproximately 20 percent. In the FIG. 12 diagram it can be seen that theoverlap in the Fourier plane of crosstalk and primary spectral ordershas been reduced substantially to zero, and the Moire pattern generatedat the output plane, assuming sufficient energy to form a pattern, willhave a spatial frequency which is twice that of the Moire patternproduced when all carriers have the same spatial frequency, as shown inP16. 9.

As stated briefly, in FIGS. 1042, by way of illustration only thecarriers for the blue and green signals have been shown as beingapproximately 20 percent greater than the carrier for the red signal; itshould be understood, however, that the degree of frequency increase ofthe augmented carriers is controlled in practice, inter alia, by thegeometry and size of the projection light source, the resolution andmodulation transfer function of the recording medium throughout therange of recorded wavelengths, and the spatial frequency bandwidth ofthe recorded scene. It can be seen, for example, from an inspection ofFIG. 10 that the area of overlap between the crosstalk and primaryspectral orders might be reduced to a greater degree than is illustratedby further increasing the Gm carrier frequency, if the modulationtransfer function of the recording medium is sufficiently flat to carrythe higher carrier frequencies without a compensating degradation ofimage resolution. It is important to note that this invention enablesthe greater sensitivity of panchromatic black-and-white emulsions in thehigher energy region to be more effectively utilized than in prior artdiffraction process systems, since by a preferred practice of thisinvention the higher frequency carriers are used to carry informationassociated with the higher energy scene information.

In accordance with another aspect of this invention, the transmission ofcrosstalk energy through spatial filter apertures designated to passprimary spectral energy may be reduced by selective adjustment of theazimuthal orientation of one or more of the spatial carriers relative tothe others. FIG. 13 illustrates, for example, that displacement of thespatial carrier for the green signal Gm such that it forms an angle of38W, rather than the nominal 45 with respect to the spatial carrier forthe red signal Rw, has the effect of decreasing the areas of overlap ofcrosstalk and primary spectral orders. It should be noted that in FIG.13, the spatial frequency of the G0) carrier has been increased by 20percent relative to the frequency of the Rm and Ba: carriers. It isevident that there is substantially less latitude in the adjustment ofcarrier orientation than in adjustment of carrier frequency sinceadjustment of the carrier azimuth beyond an optimum value will causedeterioration of the reconstructed image fidelity due to overlap ofprimary npectral orders and/or increasing overlap of crmmtalk andprimary spatial orders.

Thus, the invention teaches certain principles by which diffractionprocess multiplex recording and reconstruction systems may be devised toprovide scene reproductions of enhanced fidelity. Knowing the scenebandwidth desired to be reproduced, the source size and geometry, andcertain other parameters effecting the Fraunhofer diffraction pattern ofthe scene record which will be formed, a relative spatial frequency anazimuthal orientation of the spatial frequency and azimuthal orientationof the spatial carriers for the color signals can be determined whichwill minimize the overlap of crosstalk and primary spectral orders andthe overlap of adjacent primary spectral orders to make possiblereconstructions of enhanced saturation, resolution, and minimizeddeterioration due to Moire beat patterns.

Once the desired carrier specifications are known, an encoder as shownin FIG. 2 may be fabricated. THe encoder would, of course, have thearrays of filter elements at spatial frequencies and orientations whichcorrespond to the predetermined optimum carrier geometry. Alternatively,a multiplex recording with the desired carrier geometry may be made bysequentially exposing a photosensitive material to the component imagesto be recorded appropriately spectrally filtered and multiplied with anamplitude grating of the appropriate frequency and orientation.

Certain changes may be made in the above-described methods andstructures without departing from the true spirit and scope of theinvention herein involved. For example, whereas the invention has beendescribed as being preferably implemented by a three carrier recordingand reconstruction, the principles set forth herein are applicable tomultiplex recording and reconstruction with other than threecarriermodulating signals. It has been stressed that the abovediscussion has been maintained at a fundamental level in order that theprinciples of the invention be explained as clearly as possible andwithout undue complexity. It is contemplated that the principles of theinvention, as set forth in the above embodiments and methods, areapplicable to other and more complex systems containing various otherfiltering arrangements and multiple light sources arranged in variousgeometries, including systems using off-axis sources so located as tocause a first spectral order of each information channel to be locatedon axis. It is therefore intended that the subject matter of the abovedepiction shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

1. A method of spectral zonal photography, comprising:

exposing a photosensitive material to an additive superposition offirst, second, and third spectral separation images characterizingradiation propagating from a scene in three different spectral zones;

during the said exposure operation, causing a periodic grating functionof predetermined spatial frequency and of predetermined unique azimuthalorientation to be multiplied with each of said separation images toimpress said first, second, and third spectral separation imagesrespectively on first, second, and third spatial carriers capable ofbeing separately detected by Fourier analysis, the direction vector ofsaid second spatial carrier being intermediate the direction vectors ofsaid first and third spatial carriers, said predetermined spatialfrequency of at least one of said first and third spatial carriers beinggreater than the spatial frequency of said second spatial carrier; and

developing the exposed photosensitive material to form a record, therespective spatial frequency and orientation of said grating functionsbeing such that an optical Fourier transformation of said recordexhibits a minimum of overlap of cross-product orders with firstspectral orders of said images.

2. The method defined by claim I wherein the angular separation of saidfirst and second spatial carriers and the angular ueparation of saidsecond and third spatial carriers each lie in the range M35" 50',

3. The method defined by claim 2 wherein at least one of said angularseparations is substantially 45.

4. The method defined by claim 3 'wherein the angular separation betweeneach of said first and said second and between said second and saidthird carriers is substantially 45.

5. The method defined by claim 1 wherein the spatial frequency of saidone carrier is substantially l5-25 percent greater than the frequency ofsaid second carrier.

6. The method defined by claim 5 wherein the spatial frequency of saidone carrier is substantially 20 percent greater than the frequency ofsaid second carrier.

7. The method defined by claim 1 wherein the spatial frequency of eachof said first and third carriers is greater than the spatial frequencyof said second carrier.

8. The method defined by claim 7 wherein the spatial frequency of eachof said first and third carriers is substantially l5-25 percent greaterthan the frequency of said second carrier. I

9. The method defined by claim 2 wherein the direction vector of saidsecond spatial carrier is intermediate the direction vectors of saidfirst and third spatial carriers and wherein said predetermined spatialfrequency of at least one of said first and third carriers is greaterthan the spatial frequency of said second carrier.

10. The method defined by claim 4 wherein the direction vector of saidsecond spatial carrier is intermediate the direction vectors of saidfirst and third spatial carriers and wherein said predetermined spatialfrequency of at least one of said first and third spatial carriers isgreater than the spatial frequency of said second carrier.

11. The method defined by claim 10 wherein the spatial frequency of eachof said first and third carriers is substantially l5-25 percent greaterthan the frequency of said second carrier.

12. The method defined by claim 1 wherein said first, second, and thirdspectral separation images constitute relatively middle wavelength, longwavelength, short wavelength images, respectively, and wherein thedirection vector of said second carrier is intermediate the directionvectors of said first and third carriers.

13. The method defined by claim 1 wherein said first, second, and thirdspectral separation images constitute relatively middle wavelength, longwavelength, and short wavelength images.

14. The method defined by claim 1 wherein the said spatial carriers onwhich said first, second, and third spectral separation images areimpressed are introduced by multiplying said color separation imageswith a spectral zonal encoder comprising first, second, and thirdmutually coextensive periodic arrays of filter elements of saidpredetermined spatial frequency and unique azimuthal orientation, saidarrays of filter elements having respective preferential absorption insaid three spectral zones.

15. The method defined by claim 14 wherein the direction vector of saidsecond filter array is intermediate the direction vectors of said firstand third arrays and wherein the spatial frequency of at least one ofsaid first and third filter arrays is greater than the spatial frequencyof said second array.

16. The method defined by claim 15 wherein the angular separationsbetween said first and second filter arrays and between said second andthird arrays is substantially 45 and wherein the spatial frequency ofeach of said first and third arrays is substantially 15-25 percentgreater than the spatial frequency of said second array.

17. The method defined by claim 16 wherein said first, second, and thirdspectral separation images constitute relatively middle wavelength, longwavelength, and short wavelength images.

18. A method of spectral zonal photography and reconstruction,comprising:

exposing a photosensitive material to an additive superposition offirst, second, and third spectral separation images characterizingradiation propagating from a scene in three different spectral zones;

during the said exposure operation, causing a periodic grating functionof predetermined spatial frequency and of predetermined unique azimuthalorientation to be multiplied with each of said separation images toimpress said first, second, and third spectral separation imagesrespectively on first, second, and third spatial carriers capable ofbeing separately detected by Fourier analysis, the direction vector ofsaid second spatial carrier being intermediate the direction vectors ofsaid first and third spatial carriers, said predetermined spatialfrequency of at least one of said first and third spatial carriers beinggreater than the spatial frequency of said second spatial carrier;

developing the exposed photosensitive material to form a record, therespective spatial frequency and orientation of said grating functionsbeing such that an optical Fourier transformation of said recordexhibits a minimum of overlap of cross product terms with first spectralorders of said images;

locating the developed record in a beam of light which is substantiallycoherent at the record;

forming a Fourier transform space at least one diffraction pattern ofsaid record including three angularly separated Dirac delta functionarrays respectively convolved with spectra of said first, second, andthird spectral separation images; and

selectively transmitting at least one spectral order of each of saidarrays through said Fourier transform space to form at an output planean image of said photographed scene.

19. The method defined by claim 18 wherein the angular separation ofsaid first and second spatial carriers and the angular separation ofsaid second and third spatial carriers each lie in the range of 35-50.

20. The method defined by claim 19 wherein at least one of said angularseparations'is substantially 45.

2. The method defined by claim 20 wherein the angular separationsbetween each of said first and said second and between said second andsaid third carriers is substantially 45.

22. The method defined by claim 18 wherein the spatial frequency of saidone carrier is substantially l5-25 percent greater than the frequency ofsaid second carrier.

23. The method defined by claim 22 wherein the spatial frequency of eachof said first and third carriers is greater than the spatial frequencyof said second carrier.

24. The method defined by claim 23 wherein the spatial frequency of eachof said first and third carriers is substantially l5-25 percent greaterthan the frequency of said second carrier.

25. The method defined by claim 19 wherein the direction vector of saidsecond spatial carrier is intermediate the direction vectors of saidfirst and third spatial carriers and wherein said predetermined spatialfrequency of at least one of said first and third carriers is greaterthan the spatial frequency of said second carrier.

26. The method defined by claim 21 wherein the direction vector of saidsecond spatial carrier is intermediate the direction vectors of saidfirst and third spatial carriers and wherein said predetermined spatialfrequency of at least one of said first and third spatial carriers isgreater than the spatial frequency of said second carrier.

27. The method defined by claim 26 wherein the spatial frequency of eachof said first and third carriers is substantially 15-25 percent greaterthan the frequency of said second carrier.

28. The method defined by claim 18 wherein said first, second, and thirdspectral separation images constitute relatively middle wavelength, longwavelength. and short wavelength images, respectively, and wherein thedirection vector of said second carrier is intermediate the directionvectors of said first and third carriers.

29. The method as defined by claim 18 wherein said first, second, andthird spectral separation images constitute relatively middlewavelength, long wavelength, and short wavelength images.

30. A spectral zonal encoder for impressing first, second, and thirdspectral separation images on first, second, and third spatial carriers,respectively, comprising first, second, and third mutually coextensiveperiodic arrays of filter elements of predetermined spatial frequencyand unique azimuthal orientation, said arrays of filter elements havingrespective preferential absorption in three spectral zonescharacterizing said first, second, and third spectral separation images,the direction vector of said second filter array being intermediate thedirection vectors of said first and third arrays and the spatialfrequency of at least one of said first and third filter arrays beinggreater than the spatial frequency of said second array.

31. The encoder defined by claim 30 wherein the spatial frequency ofsaid one carrier is substantially l5-25 percent greater than thefrequency of said second carrier.

32. The encoder defined by claim 31 wherein the spatial frequency ofsaid one carrier is substantially 20 percent greater than the frequencyof said second carrier.

33. The encoder defined by claim 30 wherein the angular separationsbetween said first and second filter arrays and between said second andthird arrays is substantially 35-50 and wherein the spatial frequency ofeach of said first and third arrays is substantially 15-25 percentgreater than the spatial frequency of said second array.

34. The encoder defined by claim 33 wherein said first, second, andthird arrays of filter elements have yellow, cyan, and magenta spectralcharacteristics, respectively.

2 3 I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,640,711 Dated February 8, 1972 Inventor(s) EDMUND L. BOUCHE It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

F- Claim 18, column 8, line 23, after "forming" insert --in--; AfterClaim 20, the next claim number should be--21- Claim 23, column 8, line44, claim "22" should be Signed and sealed this L th day of July 1972.

(SEAL) Attest:

ROBERT GOTTSCHALK Commissioner of- Patents EDWARD I'LFLETCHELJR.Attesting Officer 3 3 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3,640,711 Dated February 8, 1972 Inventor(s)EDMUND L. BOUCHE It is certified that error appears in theabove-identified patent I and that said Letters Patent are herebycorrected as shown below:

F- Claim 18, column 8, line 23, after "forming" insert --in--; AfterClaim 20, the next claim number should be-2l--; Claim 23, column 8, line44, claim "22" should be Signed and sealed this L th day of July 1972.

(SEAL) Attest:

EDWARD I LFLETCHEmJR. ROBERT GOTTSCHALK Attesting Officer 7 Commissionerof Patents

2. The method defined by claim 1 wherein the angular separation of saidfirst and second spatial carriers and the angular separation of saidsecond and third spatial carriers each lie in the range of 35*-50* . 3.The method defined by claim 2 wherein at least one of said angularseparations is substantially 45*.
 4. The method defined by claim 3wherein the angular separation between each of said first and saidsecond and between said second and said third carriers is substantially45*.
 5. The method defined by claim 1 wherein the spatial frequency ofsaid one carrier is substantially 15-25 percent greater than thefrequency of said second carrier.
 6. The method defined by claim 5wherein the spatial frequency of said one carrier is substantially 20percent greater than the frequency of said second carrier.
 7. The methoddefined by claim 1 wherein the spatial frequency of each of said firstand third carriers is greater than the spatial frequency of said secondcarrier.
 8. The method defined by claim 7 wherein the spatial frequencyof each of said first and third carriers is substantially 15-25 percentgreater than the frequency of said second carrier.
 9. The method definedby claim 2 wherein the direction vector of said second spatial carrieris intermediate the direction vectors of said first and third spatialcarriers and wherein said predetermined spatial frequency of at leastone of said first and third carriers is greater than the spatialfrequency of said second carrier.
 10. The method defined by claim 4wherein the direction vector of said second spatial carrier isintermediate the direction vectors of said first and third spatialcarriers and wherein said predetermined spatial frequency of at lEastone of said first and third spatial carriers is greater than the spatialfrequency of said second carrier.
 11. The method defined by claim 10wherein the spatial frequency of each of said first and third carriersis substantially 15-25 percent greater than the frequency of said secondcarrier.
 12. The method defined by claim 1 wherein said first, second,and third spectral separation images constitute relatively middlewavelength, long wavelength, short wavelength images, respectively, andwherein the direction vector of said second carrier is intermediate thedirection vectors of said first and third carriers.
 13. The methoddefined by claim 1 wherein said first, second, and third spectralseparation images constitute relatively middle wavelength, longwavelength, and short wavelength images.
 14. The method defined by claim1 wherein the said spatial carriers on which said first, second, andthird spectral separation images are impressed are introduced bymultiplying said color separation images with a spectral zonal encodercomprising first, second, and third mutually coextensive periodic arraysof filter elements of said predetermined spatial frequency and uniqueazimuthal orientation, said arrays of filter elements having respectivepreferential absorption in said three spectral zones.
 15. The methoddefined by claim 14 wherein the direction vector of said second filterarray is intermediate the direction vectors of said first and thirdarrays and wherein the spatial frequency of at least one of said firstand third filter arrays is greater than the spatial frequency of saidsecond array.
 16. The method defined by claim 15 wherein the angularseparations between said first and second filter arrays and between saidsecond and third arrays is substantially 45* and wherein the spatialfrequency of each of said first and third arrays is substantially 15-25percent greater than the spatial frequency of said second array.
 17. Themethod defined by claim 16 wherein said first, second, and thirdspectral separation images constitute relatively middle wavelength, longwavelength, and short wavelength images.
 18. A method of spectral zonalphotography and reconstruction, comprising: exposing a photosensitivematerial to an additive superposition of first, second, and thirdspectral separation images characterizing radiation propagating from ascene in three different spectral zones; during the said exposureoperation, causing a periodic grating function of predetermined spatialfrequency and of predetermined unique azimuthal orientation to bemultiplied with each of said separation images to impress said first,second, and third spectral separation images respectively on first,second, and third spatial carriers capable of being separately detectedby Fourier analysis, the direction vector of said second spatial carrierbeing intermediate the direction vectors of said first and third spatialcarriers, said predetermined spatial frequency of at least one of saidfirst and third spatial carriers being greater than the spatialfrequency of said second spatial carrier; developing the exposedphotosensitive material to form a record, the respective spatialfrequency and orientation of said grating functions being such that anoptical Fourier transformation of said record exhibits a minimum ofoverlap of cross product terms with first spectral orders of saidimages; locating the developed record in a beam of light which issubstantially coherent at the record; forming a Fourier transform spaceat least one diffraction pattern of said record including threeangularly separated Dirac delta function arrays respectively convolvedwith spectra of said first, second, and third spectral separationimages; and selectively transmitting at least one spectral order of eachof said arrays through said Fourier transform space to form at an outputplane an image of said photographed scene.
 19. The method defined byclaim 18 wherein the angular separation of said first and second spatialcarriers and the angular separation of said second and third spatialcarriers each lie in the range of 35*-50* .
 20. The method defined byclaim 19 wherein at least one of said angular separations issubstantially 45*.
 22. The method defined by claim 20 wherein theangular separations between each of said first and said second andbetween said second and said third carriers is substantially 45* . 22.The method defined by claim 18 wherein the spatial frequency of said onecarrier is substantially 15-25 percent greater than the frequency ofsaid second carrier.
 23. The method defined by claim 22 wherein thespatial frequency of each of said first and third carriers is greaterthan the spatial frequency of said second carrier.
 24. The methoddefined by claim 23 wherein the spatial frequency of each of said firstand third carriers is substantially 15-25 percent greater than thefrequency of said second carrier.
 25. The method defined by claim 19wherein the direction vector of said second spatial carrier isintermediate the direction vectors of said first and third spatialcarriers and wherein said predetermined spatial frequency of at leastone of said first and third carriers is greater than the spatialfrequency of said second carrier.
 26. The method defined by claim 21wherein the direction vector of said second spatial carrier isintermediate the direction vectors of said first and third spatialcarriers and wherein said predetermined spatial frequency of at leastone of said first and third spatial carriers is greater than the spatialfrequency of said second carrier.
 27. The method defined by claim 26wherein the spatial frequency of each of said first and third carriersis substantially 15-25 percent greater than the frequency of said secondcarrier.
 28. The method defined by claim 18 wherein said first, second,and third spectral separation images constitute relatively middlewavelength, long wavelength, and short wavelength images, respectively,and wherein the direction vector of said second carrier is intermediatethe direction vectors of said first and third carriers.
 29. The methodas defined by claim 18 wherein said first, second, and third spectralseparation images constitute relatively middle wavelength, longwavelength, and short wavelength images.
 30. A spectral zonal encoderfor impressing first, second, and third spectral separation images onfirst, second, and third spatial carriers, respectively, comprisingfirst, second, and third mutually coextensive periodic arrays of filterelements of predetermined spatial frequency and unique azimuthalorientation, said arrays of filter elements having respectivepreferential absorption in three spectral zones characterizing saidfirst, second, and third spectral separation images, the directionvector of said second filter array being intermediate the directionvectors of said first and third arrays and the spatial frequency of atleast one of said first and third filter arrays being greater than thespatial frequency of said second array.
 31. The encoder defined by claim30 wherein the spatial frequency of said one carrier is substantially15-25 percent greater than the frequency of said second carrier.
 32. Theencoder defined by claim 31 wherein the spatial frequency of said onecarrier is substantially 20 percent greater than the frequency of saidsecond carrier.
 33. The encoder defined by claim 30 wherein the angularseparations between said first and second filter arrays and between saidsecond and third arrays is substantially 35*-50* and wherein the spatialfrequency of each of said first and third arrays is substantially 15-25percent greater than the spatial frequency of said second array.
 34. Theencoder defined by claim 33 wherein said first, second, and third arRaysof filter elements have yellow, cyan, and magenta spectralcharacteristics, respectively.